From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jason Penilla <11360596+jpenilla@users.noreply.github.com>
Date: Sun, 20 Jun 2021 18:19:09 -0700
Subject: [PATCH] Deobfuscate stacktraces in log messages, crash reports, and
 etc.


diff --git a/build.gradle.kts b/build.gradle.kts
index fd4b0c173be72516f22c6e5d540249e3079a7216..cf6c265714d8241f52e83de59094d7ae2cd56884 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -1,4 +1,6 @@
+import io.papermc.paperweight.tasks.BaseTask
 import io.papermc.paperweight.util.*
+import java.nio.file.Files
 
 plugins {
     java
@@ -8,6 +10,11 @@ plugins {
 
 repositories {
     maven("https://libraries.minecraft.net/")
+    // Paper start
+    maven("https://maven.fabricmc.net/") {
+        mavenContent { includeModule("net.fabricmc", "mapping-io") }
+    }
+    // Paper end
 }
 
 dependencies {
@@ -23,6 +30,7 @@ dependencies {
           Scanning takes about 1-2 seconds so adding this speeds up the server start.
      */
     implementation("org.apache.logging.log4j:log4j-core:2.14.1") // Paper - implementation
+    annotationProcessor("org.apache.logging.log4j:log4j-core:2.14.1") // Paper - Needed to generate meta for our Log4j plugins
     // Paper end
     implementation("org.apache.logging.log4j:log4j-iostreams:2.17.1") // Paper
     implementation("org.ow2.asm:asm:9.2")
@@ -35,6 +43,8 @@ dependencies {
     runtimeOnly("org.apache.maven.resolver:maven-resolver-connector-basic:1.7.2")
     runtimeOnly("org.apache.maven.resolver:maven-resolver-transport-http:1.7.2")
 
+    implementation("net.fabricmc:mapping-io:0.3.0") // Paper - needed to read mappings for stacktrace deobfuscation
+
     testImplementation("junit:junit:4.13.2")
     testImplementation("org.hamcrest:hamcrest-library:1.3")
 }
@@ -92,6 +102,45 @@ tasks.shadowJar {
     }
 }
 
+// Paper start - include reobf mappings in jar for stacktrace deobfuscation
+abstract class IncludeMappings : BaseTask() {
+    @get:InputFile
+    abstract val inputJar: RegularFileProperty
+
+    @get:InputFile
+    abstract val mappings: RegularFileProperty
+
+    @get:OutputFile
+    abstract val outputJar: RegularFileProperty
+
+    override fun init() {
+        super.init()
+        outputJar.convention(defaultOutput())
+    }
+
+    @TaskAction
+    private fun addMappings() {
+        outputJar.get().asFile.parentFile.mkdirs()
+        inputJar.get().asFile.copyTo(outputJar.get().asFile, overwrite = true)
+        outputJar.get().path.openZip().use { fs ->
+            val dir = fs.getPath("META-INF/mappings/")
+            Files.createDirectories(dir)
+            val target = dir.resolve("reobf.tiny")
+            Files.copy(mappings.path, target)
+        }
+    }
+}
+
+val includeMappings = tasks.register<IncludeMappings>("includeMappings") {
+    inputJar.set(tasks.fixJarForReobf.flatMap { it.outputJar })
+    mappings.set(tasks.reobfJar.flatMap { it.mappingsFile })
+}
+
+tasks.reobfJar {
+    inputJar.set(includeMappings.flatMap { it.outputJar })
+}
+// Paper end - include reobf mappings in jar for stacktrace deobfuscation
+
 tasks.test {
     exclude("org/bukkit/craftbukkit/inventory/ItemStack*Test.class")
 }
diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index fda5a623ec6bba0ed4d230415f7b9779ee2e8ccf..af43c63df3c82e910b77afd2a8899b8e6fc6db6d 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -430,4 +430,9 @@ public class PaperConfig {
             log("Async Chunks: Enabled - Chunks will be loaded much faster, without lag.");
         }
     }
+
+    public static boolean deobfuscateStacktraces = true;
+    private static void loggerSettings() {
+        deobfuscateStacktraces = getBoolean("settings.loggers.deobfuscate-stacktraces", deobfuscateStacktraces);
+    }
 }
diff --git a/src/main/java/com/destroystokyo/paper/io/SyncLoadFinder.java b/src/main/java/com/destroystokyo/paper/io/SyncLoadFinder.java
index 0bb4aaa546939b67a5d22865190f30478a9337c1..d3e619655382e50e9ac9323ed942502d85c9599c 100644
--- a/src/main/java/com/destroystokyo/paper/io/SyncLoadFinder.java
+++ b/src/main/java/com/destroystokyo/paper/io/SyncLoadFinder.java
@@ -91,7 +91,7 @@ public class SyncLoadFinder {
 
                 final JsonArray traces = new JsonArray();
 
-                for (StackTraceElement element : pair.getFirst().stacktrace) {
+                for (StackTraceElement element : io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(pair.getFirst().stacktrace)) {
                     traces.add(String.valueOf(element));
                 }
 
diff --git a/src/main/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java b/src/main/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java
new file mode 100644
index 0000000000000000000000000000000000000000..c701ef3c287f62aa0ebfbdbd6da6ed82a1c7793c
--- /dev/null
+++ b/src/main/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java
@@ -0,0 +1,38 @@
+package io.papermc.paper.logging;
+
+import io.papermc.paper.util.StacktraceDeobfuscator;
+import org.apache.logging.log4j.core.Core;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.appender.rewrite.RewritePolicy;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.PluginFactory;
+import org.apache.logging.log4j.core.impl.Log4jLogEvent;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+@Plugin(
+    name = "StacktraceDeobfuscatingRewritePolicy",
+    category = Core.CATEGORY_NAME,
+    elementType = "rewritePolicy",
+    printObject = true
+)
+public final class StacktraceDeobfuscatingRewritePolicy implements RewritePolicy {
+    private StacktraceDeobfuscatingRewritePolicy() {
+    }
+
+    @Override
+    public @NonNull LogEvent rewrite(final @NonNull LogEvent rewrite) {
+        final Throwable thrown = rewrite.getThrown();
+        if (thrown != null) {
+            StacktraceDeobfuscator.INSTANCE.deobfuscateThrowable(thrown);
+            return new Log4jLogEvent.Builder(rewrite)
+                .setThrownProxy(null)
+                .build();
+        }
+        return rewrite;
+    }
+
+    @PluginFactory
+    public static @NonNull StacktraceDeobfuscatingRewritePolicy createPolicy() {
+        return new StacktraceDeobfuscatingRewritePolicy();
+    }
+}
diff --git a/src/main/java/io/papermc/paper/util/ObfHelper.java b/src/main/java/io/papermc/paper/util/ObfHelper.java
new file mode 100644
index 0000000000000000000000000000000000000000..b8b17d046f836c8652ab094db00ab1af84971b2c
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/ObfHelper.java
@@ -0,0 +1,146 @@
+package io.papermc.paper.util;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import net.fabricmc.mappingio.MappingReader;
+import net.fabricmc.mappingio.format.MappingFormat;
+import net.fabricmc.mappingio.tree.MappingTree;
+import net.fabricmc.mappingio.tree.MemoryMappingTree;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public enum ObfHelper {
+    INSTANCE;
+
+    public static final String MOJANG_PLUS_YARN_NAMESPACE = "mojang+yarn";
+    public static final String SPIGOT_NAMESPACE = "spigot";
+
+    private final @Nullable Map<String, ClassMapping> mappingsByObfName;
+    private final @Nullable Map<String, ClassMapping> mappingsByMojangName;
+
+    ObfHelper() {
+        final @Nullable Set<ClassMapping> maps = loadMappingsIfPresent();
+        if (maps != null) {
+            this.mappingsByObfName = maps.stream().collect(Collectors.toUnmodifiableMap(ClassMapping::obfName, map -> map));
+            this.mappingsByMojangName = maps.stream().collect(Collectors.toUnmodifiableMap(ClassMapping::mojangName, map -> map));
+        } else {
+            this.mappingsByObfName = null;
+            this.mappingsByMojangName = null;
+        }
+    }
+
+    public @Nullable Map<String, ClassMapping> mappingsByObfName() {
+        return this.mappingsByObfName;
+    }
+
+    public @Nullable Map<String, ClassMapping> mappingsByMojangName() {
+        return this.mappingsByMojangName;
+    }
+
+    /**
+     * Attempts to get the obf name for a given class by its Mojang name. Will
+     * return the input string if mappings are not present.
+     *
+     * @param fullyQualifiedMojangName fully qualified class name (dotted)
+     * @return mapped or original fully qualified (dotted) class name
+     */
+    public String reobfClassName(final String fullyQualifiedMojangName) {
+        if (this.mappingsByMojangName == null) {
+            return fullyQualifiedMojangName;
+        }
+
+        final ClassMapping map = this.mappingsByMojangName.get(fullyQualifiedMojangName);
+        if (map == null) {
+            return fullyQualifiedMojangName;
+        }
+
+        return map.obfName();
+    }
+
+    /**
+     * Attempts to get the Mojang name for a given class by its obf name. Will
+     * return the input string if mappings are not present.
+     *
+     * @param fullyQualifiedObfName fully qualified class name (dotted)
+     * @return mapped or original fully qualified (dotted) class name
+     */
+    public String deobfClassName(final String fullyQualifiedObfName) {
+        if (this.mappingsByObfName == null) {
+            return fullyQualifiedObfName;
+        }
+
+        final ClassMapping map = this.mappingsByObfName.get(fullyQualifiedObfName);
+        if (map == null) {
+            return fullyQualifiedObfName;
+        }
+
+        return map.mojangName();
+    }
+
+    private static @Nullable Set<ClassMapping> loadMappingsIfPresent() {
+        try (final @Nullable InputStream mappingsInputStream = ObfHelper.class.getClassLoader().getResourceAsStream("META-INF/mappings/reobf.tiny")) {
+            if (mappingsInputStream == null) {
+                return null;
+            }
+            final MemoryMappingTree tree = new MemoryMappingTree();
+            MappingReader.read(new InputStreamReader(mappingsInputStream, StandardCharsets.UTF_8), MappingFormat.TINY_2, tree);
+            final Set<ClassMapping> classes = new HashSet<>();
+
+            final StringPool pool = new StringPool();
+            for (final MappingTree.ClassMapping cls : tree.getClasses()) {
+                final Map<String, String> methods = new HashMap<>();
+
+                for (final MappingTree.MethodMapping methodMapping : cls.getMethods()) {
+                    methods.put(
+                        pool.string(methodKey(
+                            methodMapping.getName(SPIGOT_NAMESPACE),
+                            methodMapping.getDesc(SPIGOT_NAMESPACE)
+                        )),
+                        pool.string(methodMapping.getName(MOJANG_PLUS_YARN_NAMESPACE))
+                    );
+                }
+
+                final ClassMapping map = new ClassMapping(
+                    cls.getName(SPIGOT_NAMESPACE).replace('/', '.'),
+                    cls.getName(MOJANG_PLUS_YARN_NAMESPACE).replace('/', '.'),
+                    Map.copyOf(methods)
+                );
+                classes.add(map);
+            }
+
+            return Set.copyOf(classes);
+        } catch (final IOException ex) {
+            System.err.println("Failed to load mappings for stacktrace deobfuscation.");
+            ex.printStackTrace();
+            return null;
+        }
+    }
+
+    public static String methodKey(final String obfName, final String obfDescriptor) {
+        return obfName + obfDescriptor;
+    }
+
+    private static final class StringPool {
+        private final Map<String, String> pool = new HashMap<>();
+
+        public String string(final String string) {
+            return this.pool.computeIfAbsent(string, Function.identity());
+        }
+    }
+
+    public record ClassMapping(
+        String obfName,
+        String mojangName,
+        Map<String, String> methodsByObf
+    ) {}
+}
diff --git a/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
new file mode 100644
index 0000000000000000000000000000000000000000..3c3051c2917548faf7e72276fb642202b33d1794
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
@@ -0,0 +1,163 @@
+package io.papermc.paper.util;
+
+import com.destroystokyo.paper.PaperConfig;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
+import it.unimi.dsi.fastutil.ints.IntList;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.Label;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+@DefaultQualifier(NonNull.class)
+public enum StacktraceDeobfuscator {
+    INSTANCE;
+
+    private final Map<Class<?>, Map<String, IntList>> lineMapCache = Collections.synchronizedMap(new LinkedHashMap<>(128, 0.75f, true) {
+        @Override
+        protected boolean removeEldestEntry(final Map.Entry<Class<?>, Map<String, IntList>> eldest) {
+            return this.size() > 127;
+        }
+    });
+
+    public void deobfuscateThrowable(final Throwable throwable) {
+        if (!PaperConfig.deobfuscateStacktraces) {
+            return;
+        }
+
+        throwable.setStackTrace(this.deobfuscateStacktrace(throwable.getStackTrace()));
+        final Throwable cause = throwable.getCause();
+        if (cause != null) {
+            this.deobfuscateThrowable(cause);
+        }
+        for (final Throwable suppressed : throwable.getSuppressed()) {
+            this.deobfuscateThrowable(suppressed);
+        }
+    }
+
+    public StackTraceElement[] deobfuscateStacktrace(final StackTraceElement[] traceElements) {
+        if (!PaperConfig.deobfuscateStacktraces) {
+            return traceElements;
+        }
+
+        final @Nullable Map<String, ObfHelper.ClassMapping> mappings = ObfHelper.INSTANCE.mappingsByObfName();
+        if (mappings == null || traceElements.length == 0) {
+            return traceElements;
+        }
+        final StackTraceElement[] result = new StackTraceElement[traceElements.length];
+        for (int i = 0; i < traceElements.length; i++) {
+            final StackTraceElement element = traceElements[i];
+
+            final String className = element.getClassName();
+            final String methodName = element.getMethodName();
+
+            final ObfHelper.ClassMapping classMapping = mappings.get(className);
+            if (classMapping == null) {
+                result[i] = element;
+                continue;
+            }
+
+            final Class<?> clazz;
+            try {
+                clazz = Class.forName(className);
+            } catch (final ClassNotFoundException ex) {
+                throw new RuntimeException(ex);
+            }
+            final @Nullable String methodKey = this.determineMethodForLine(clazz, element.getLineNumber());
+            final @Nullable String mappedMethodName = methodKey == null ? null : classMapping.methodsByObf().get(methodKey);
+
+            result[i] = new StackTraceElement(
+                element.getClassLoaderName(),
+                element.getModuleName(),
+                element.getModuleVersion(),
+                classMapping.mojangName(),
+                mappedMethodName != null ? mappedMethodName : methodName,
+                sourceFileName(classMapping.mojangName()),
+                element.getLineNumber()
+            );
+        }
+        return result;
+    }
+
+    private @Nullable String determineMethodForLine(final Class<?> clazz, final int lineNumber) {
+        final Map<String, IntList> lineMap = this.lineMapCache.computeIfAbsent(clazz, StacktraceDeobfuscator::buildLineMap);
+        for (final var entry : lineMap.entrySet()) {
+            final String methodKey = entry.getKey();
+            final IntList lines = entry.getValue();
+            for (int i = 0, linesSize = lines.size(); i < linesSize; i++) {
+                final int num = lines.getInt(i);
+                if (num == lineNumber) {
+                    return methodKey;
+                }
+            }
+        }
+        return null;
+    }
+
+    private static String sourceFileName(final String fullClassName) {
+        final int dot = fullClassName.lastIndexOf('.');
+        final String className = dot == -1
+            ? fullClassName
+            : fullClassName.substring(dot + 1);
+        final String rootClassName = className.split("\\$")[0];
+        return rootClassName + ".java";
+    }
+
+    private static Map<String, IntList> buildLineMap(final Class<?> key) {
+        final Map<String, IntList> lineMap = new HashMap<>();
+        final class LineCollectingMethodVisitor extends MethodVisitor {
+            private final IntList lines = new IntArrayList();
+            private final String name;
+            private final String descriptor;
+
+            LineCollectingMethodVisitor(String name, String descriptor) {
+                super(Opcodes.ASM9);
+                this.name = name;
+                this.descriptor = descriptor;
+            }
+
+            @Override
+            public void visitLineNumber(int line, Label start) {
+                super.visitLineNumber(line, start);
+                this.lines.add(line);
+            }
+
+            @Override
+            public void visitEnd() {
+                super.visitEnd();
+                lineMap.put(ObfHelper.methodKey(this.name, this.descriptor), this.lines);
+            }
+        }
+        final ClassVisitor classVisitor = new ClassVisitor(Opcodes.ASM9) {
+            @Override
+            public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+                return new LineCollectingMethodVisitor(name, descriptor);
+            }
+        };
+        try {
+            final @Nullable InputStream inputStream = StacktraceDeobfuscator.class.getClassLoader()
+                .getResourceAsStream(key.getName().replace('.', '/') + ".class");
+            if (inputStream == null) {
+                throw new IllegalStateException("Could not find class file: " + key.getName());
+            }
+            final byte[] classData;
+            try (inputStream) {
+                classData = inputStream.readAllBytes();
+            }
+            final ClassReader reader = new ClassReader(classData);
+            reader.accept(classVisitor, 0);
+        } catch (final IOException ex) {
+            throw new RuntimeException(ex);
+        }
+        return lineMap;
+    }
+}
diff --git a/src/main/java/io/papermc/paper/util/TraceUtil.java b/src/main/java/io/papermc/paper/util/TraceUtil.java
index 2d5494d2813b773e60ddba6790b750a9a08f21f8..7695bf44503f161523ea612ef8a884ae574a2e21 100644
--- a/src/main/java/io/papermc/paper/util/TraceUtil.java
+++ b/src/main/java/io/papermc/paper/util/TraceUtil.java
@@ -6,13 +6,15 @@ public final class TraceUtil {
 
     public static void dumpTraceForThread(Thread thread, String reason) {
         Bukkit.getLogger().warning(thread.getName() + ": " + reason);
-        StackTraceElement[] trace = thread.getStackTrace();
+        StackTraceElement[] trace = StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(thread.getStackTrace());
         for (StackTraceElement traceElement : trace) {
             Bukkit.getLogger().warning("\tat " + traceElement);
         }
     }
 
     public static void dumpTraceForThread(String reason) {
-        new Throwable(reason).printStackTrace();
+        final Throwable throwable = new Throwable(reason);
+        StacktraceDeobfuscator.INSTANCE.deobfuscateThrowable(throwable);
+        throwable.printStackTrace();
     }
 }
diff --git a/src/main/java/net/minecraft/CrashReport.java b/src/main/java/net/minecraft/CrashReport.java
index 4dd14d73a37b32288a64fbd67ee22c435b6e6d57..1a859fef0848cf23a672012e9764965ae1c07ec5 100644
--- a/src/main/java/net/minecraft/CrashReport.java
+++ b/src/main/java/net/minecraft/CrashReport.java
@@ -30,6 +30,7 @@ public class CrashReport {
     private final SystemReport systemReport = new SystemReport();
 
     public CrashReport(String message, Throwable cause) {
+        io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateThrowable(cause); // Paper
         this.title = message;
         this.exception = cause;
         this.systemReport.setDetail("CraftBukkit Information", new org.bukkit.craftbukkit.CraftCrashReport()); // CraftBukkit
diff --git a/src/main/java/net/minecraft/CrashReportCategory.java b/src/main/java/net/minecraft/CrashReportCategory.java
index 3941e14d1c3e6e688e28904948039c8b2200de5f..a4fda4a3bae9ce600e778b44cd3ef432a8b65667 100644
--- a/src/main/java/net/minecraft/CrashReportCategory.java
+++ b/src/main/java/net/minecraft/CrashReportCategory.java
@@ -104,6 +104,7 @@ public class CrashReportCategory {
         } else {
             this.stackTrace = new StackTraceElement[stackTraceElements.length - 3 - ignoredCallCount];
             System.arraycopy(stackTraceElements, 3 + ignoredCallCount, this.stackTrace, 0, this.stackTrace.length);
+            this.stackTrace = io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(this.stackTrace); // Paper
             return this.stackTrace.length;
         }
     }
diff --git a/src/main/java/net/minecraft/network/Connection.java b/src/main/java/net/minecraft/network/Connection.java
index a0d3d9e344f530b713167d0663634c40eefce5b5..c469688c2b55b1c93435a2ac6e8e4494ab7e5229 100644
--- a/src/main/java/net/minecraft/network/Connection.java
+++ b/src/main/java/net/minecraft/network/Connection.java
@@ -66,13 +66,13 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
     });
     public static final AttributeKey<ConnectionProtocol> ATTRIBUTE_PROTOCOL = AttributeKey.valueOf("protocol");
     public static final LazyLoadedValue<NioEventLoopGroup> NETWORK_WORKER_GROUP = new LazyLoadedValue<>(() -> {
-        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Client IO #%d").setDaemon(true).build());
+        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final LazyLoadedValue<EpollEventLoopGroup> NETWORK_EPOLL_WORKER_GROUP = new LazyLoadedValue<>(() -> {
-        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Client IO #%d").setDaemon(true).build());
+        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final LazyLoadedValue<DefaultEventLoopGroup> LOCAL_WORKER_GROUP = new LazyLoadedValue<>(() -> {
-        return new DefaultEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Local Client IO #%d").setDaemon(true).build());
+        return new DefaultEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Local Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     private final PacketFlow receiving;
     private final Queue<Connection.PacketHolder> queue = Queues.newConcurrentLinkedQueue();
diff --git a/src/main/java/net/minecraft/network/protocol/game/ServerboundChatPacket.java b/src/main/java/net/minecraft/network/protocol/game/ServerboundChatPacket.java
index 5165170e3289fe3939497c56a71eae9fdaa4bcfa..8a0ced3f9b9099913ade4b71181aff6cafbc4ee6 100644
--- a/src/main/java/net/minecraft/network/protocol/game/ServerboundChatPacket.java
+++ b/src/main/java/net/minecraft/network/protocol/game/ServerboundChatPacket.java
@@ -27,7 +27,7 @@ public class ServerboundChatPacket implements Packet<ServerGamePacketListener> {
 
     // Spigot Start
     private static final java.util.concurrent.ExecutorService executors = java.util.concurrent.Executors.newCachedThreadPool(
-            new com.google.common.util.concurrent.ThreadFactoryBuilder().setDaemon( true ).setNameFormat( "Async Chat Thread - #%d" ).build() );
+            new com.google.common.util.concurrent.ThreadFactoryBuilder().setDaemon( true ).setNameFormat( "Async Chat Thread - #%d" ).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(net.minecraft.server.MinecraftServer.LOGGER)).build() ); // Paper
     public void handle(final ServerGamePacketListener listener) {
         if ( !this.message.startsWith("/") )
         {
diff --git a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
index d0d058287fc1e87e944e99d4fc2cbd38eafb82b3..cec0082718c2a729044d6f19d74b8e4425816725 100644
--- a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
+++ b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
@@ -215,6 +215,7 @@ public class DedicatedServer extends MinecraftServer implements ServerInterface
         }
         com.destroystokyo.paper.PaperConfig.registerCommands();
         com.destroystokyo.paper.VersionHistoryManager.INSTANCE.getClass(); // load version history now
+        io.papermc.paper.util.ObfHelper.INSTANCE.getClass(); // load mappings for stacktrace deobf and etc.
         // Paper end
 
         this.setPvpAllowed(dedicatedserverproperties.pvp);
diff --git a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
index 7c820a8f9ae85eb6941dce0e6296775fb331d720..888e863b6d605bf587d0c071795a43d2157afa4d 100644
--- a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
+++ b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
@@ -52,10 +52,10 @@ public class ServerConnectionListener {
 
     private static final Logger LOGGER = LogUtils.getLogger();
     public static final LazyLoadedValue<NioEventLoopGroup> SERVER_EVENT_GROUP = new LazyLoadedValue<>(() -> {
-        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Server IO #%d").setDaemon(true).build());
+        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Server IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final LazyLoadedValue<EpollEventLoopGroup> SERVER_EPOLL_EVENT_GROUP = new LazyLoadedValue<>(() -> {
-        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Server IO #%d").setDaemon(true).build());
+        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Server IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     final MinecraftServer server;
     public volatile boolean running;
diff --git a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftAsyncScheduler.java b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftAsyncScheduler.java
index 3c1992e212a6d6f1db4d5b807b38d71913619fc0..9c1aff17aabd062640e3f451a2ef8c50a7c62f10 100644
--- a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftAsyncScheduler.java
+++ b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftAsyncScheduler.java
@@ -40,9 +40,9 @@ public class CraftAsyncScheduler extends CraftScheduler {
 
     private final ThreadPoolExecutor executor = new ThreadPoolExecutor(
             4, Integer.MAX_VALUE,30L, TimeUnit.SECONDS, new SynchronousQueue<>(),
-            new ThreadFactoryBuilder().setNameFormat("Craft Scheduler Thread - %1$d").build());
+            new ThreadFactoryBuilder().setNameFormat("Craft Scheduler Thread - %1$d").setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(net.minecraft.server.MinecraftServer.LOGGER)).build()); // Paper
     private final Executor management = Executors.newSingleThreadExecutor(new ThreadFactoryBuilder()
-            .setNameFormat("Craft Async Scheduler Management Thread").build());
+            .setNameFormat("Craft Async Scheduler Management Thread").setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(net.minecraft.server.MinecraftServer.LOGGER)).build()); // Paper
     private final List<CraftTask> temp = new ArrayList<>();
 
     CraftAsyncScheduler() {
diff --git a/src/main/java/org/spigotmc/WatchdogThread.java b/src/main/java/org/spigotmc/WatchdogThread.java
index 4d271cae88c16ed2419f896c728fdff612540500..dcfbe77bdb25d9c58ffb7b75c48bdb580bc0de47 100644
--- a/src/main/java/org/spigotmc/WatchdogThread.java
+++ b/src/main/java/org/spigotmc/WatchdogThread.java
@@ -106,7 +106,7 @@ public class WatchdogThread extends Thread
                     log.log( Level.SEVERE, "During the run of the server, a plugin set an excessive velocity on an entity" );
                     log.log( Level.SEVERE, "This may be the cause of the issue, or it may be entirely unrelated" );
                     log.log( Level.SEVERE, org.bukkit.craftbukkit.CraftServer.excessiveVelEx.getMessage());
-                    for ( StackTraceElement stack : org.bukkit.craftbukkit.CraftServer.excessiveVelEx.getStackTrace() )
+                    for ( StackTraceElement stack : io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(org.bukkit.craftbukkit.CraftServer.excessiveVelEx.getStackTrace()) ) // Paper
                     {
                         log.log( Level.SEVERE, "\t\t" + stack );
                     }
@@ -194,7 +194,7 @@ public class WatchdogThread extends Thread
         }
         log.log( Level.SEVERE, "\tStack:" );
         //
-        for ( StackTraceElement stack : thread.getStackTrace() )
+        for ( StackTraceElement stack : io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(thread.getStackTrace()) ) // Paper
         {
             log.log( Level.SEVERE, "\t\t" + stack );
         }
diff --git a/src/main/resources/log4j2.xml b/src/main/resources/log4j2.xml
index d285dbec16272db6b8a71865e05924ad66087407..1a05d23ff886b015fb9396f119822c678a47ec6f 100644
--- a/src/main/resources/log4j2.xml
+++ b/src/main/resources/log4j2.xml
@@ -30,10 +30,14 @@
             <DefaultRolloverStrategy max="1000"/>
         </RollingRandomAccessFile>
         <Async name="Async">
+            <AppenderRef ref="rewrite"/>
+        </Async>
+        <Rewrite name="rewrite">
+            <StacktraceDeobfuscatingRewritePolicy />
             <AppenderRef ref="File"/>
             <AppenderRef ref="TerminalConsole" level="info"/>
             <AppenderRef ref="ServerGuiConsole" level="info"/>
-        </Async>
+        </Rewrite>
     </Appenders>
     <Loggers>
         <Root level="info">
